Studies of microorganisms in pure laboratory culture for over a century have delivered fruitful insights into microbial genetics and physiology, underpinning biotechnology, and molecular biology. Yet most bacteria cannot be or have not been cultured under laboratory conditions. Microorganisms in their natural environments live in complex, mixed, and interdependent microbial communities (e.g. in soil, feces, sewage, rivers, oceans), with key roles in the biosphere. These systems are intimately connected with the big challenges for the future of human existence: agriculture and food production, diet and health, and impact of human communities on the natural environment. Knowledge and understanding of the biodiversity of bacteria is minimal in comparison with the diversity of higher plants and animals, where perhaps 90–99% of all species are known. In stark contrast, it is estimated that less than 1% of bacterial diversity is known. Even in the human microbial ecosystem, which has...